When David Ulevitch was still a student at Washington University in St. Louis, in 2001, he started a company that would become one of the biggest free domain name providers in the world. But because EveryDNS was available for free, Ulevitch says, it attracted much of the "underbelly of the Internet"--meaning the scammers, spammers, and bot masters who posed a security risk to everyday Internet users.

"All the bad guys were using our service," the 32-year-old Ulevitch says. "So we became very good at detecting when they were, and rerouting their traffic." He also accumulated a massive amount of data and insight involving those bad actors. And that set the stage for Ulevitch's second startup, OpenDNS. Though EveryDNS found ways to stifle malicious users, OpenDNS "turns DNS on its head" by using it as a way for people to access the Internet. Using the massive amounts of data the company has on hand, OpenDNS then protects users from malware, phishing sites, and other online security threats.

This approach to security represents a massive disruption, Ulevitch says. Security has traditionally been appliance-driven. Computers are plugged into security appliances you see in IT departments at home or in the workplace, and that machine does what it needs to do to protect your computer. OpenDNS's cloud-based approach to security eliminates such hardware, and addresses the needs of a work force that increasingly operates remotely and accesses cloud-based services from a variety of mobile devices.

OpenDNS has 50 million daily users, Ulevitch says, including consumers who access the service as part of their at-home security systems, and its Umbrella enterprise system, sold to businesses. Ulevitch sold EveryDNS, the first startup, in 2010 to New Hampshire DNS servicer Dyn, which handles traffic management for large companies including Twitter and Netflix.

Dyn CEO Jeremy Hitchcock calls Ulevitch a "visionary" with a "great technical mind" who understands the Internet's inner workings better than most. "I mean [he] really get into the weeds," Hitchcock says. "OpenDNS is a great example of that. The DNS layer of the Internet has a lot of potential."

Clearly, investors agree with that assessment. The company recently raised $35 million in Series C financing with participation from networking giant Cisco. That brings total funding to a whopping $53 million.

With the cloud now a part of everyday life, OpenDNS's model has attracted the attention of many big security companies, says Ulevitch. And though some have opted to partner with Ulevitch, others are looking to mimic OpenDNS's solutions. As OpenDNS matures alongside the cloud, maintaining the company's footing becomes Ulevitch's top priority as founder and CEO--marking a big difference from the years spent alone ahead of the curve.

"It's a validation of our approach," he says. But being at the cutting edge of new ways to do security presents a new problem. "It's much easier to run a company when you're in second place," he says.